<?php
/**
 * Printemps Framework Markdown 解析类
 * Printemp Framewprk Extendstion
 * PF 拓展
 */

/**
 * Markdown解析
 * Copyright (c) 2014 Typecho team (http://www.typecho.org)
 * GNU General Public License 2.0
 */
class MarkdownConvert
{ 
    /**
     * convert 
     * 
     * @param string $text 
     * @return string
     */
    public static function convert($text)
    {
        static $parser;

        if (empty($parser)) {
            $parser = new MarkdownExtraExtended();
        }

        return $parser->transform($text);
    }
}

#
# Markdown  -  A text-to-HTML conversion tool for web writers
#
# PHP Markdown  
# Copyright (c) 2004-2013 Michel Fortin  
# <http://michelf.com/projects/php-markdown/>
#
# Original Markdown  
# Copyright (c) 2004-2006 John Gruber  
# <http://daringfireball.net/projects/markdown/>
#

#
# Markdown Parser Class
#

class _Markdown {

    ### Version ###

    const  MARKDOWNLIB_VERSION  =  "1.3";   

    ### Configuration Variables ###

    # Change to ">" for HTML output.
    public $empty_element_suffix = " />";
    public $tab_width = 4;
    
    # Change to `true` to disallow markup or entities.
    public $no_markup = false;
    public $no_entities = false;
    
    # Predefined urls and titles for reference links and images.
    public $predef_urls = array();
    public $predef_titles = array();


    ### Parser Implementation ###

    # Regex to match balanced [brackets].
    # Needed to insert a maximum bracked depth while converting to PHP.
    protected $nested_brackets_depth = 6;
    protected $nested_brackets_re;
    
    protected $nested_url_parenthesis_depth = 4;
    protected $nested_url_parenthesis_re;

    # Table of hash values for escaped characters:
    protected $escape_chars = '\`*_{}[]()>#+-.!';
    protected $escape_chars_re;


    public function __construct() {
    #
    # Constructor function. Initialize appropriate member variables.
    #
        $this->_initDetab();
        $this->prepareItalicsAndBold();
    
        $this->nested_brackets_re = 
            str_repeat('(?>[^\[\]]+|\[', $this->nested_brackets_depth).
            str_repeat('\])*', $this->nested_brackets_depth);
    
        $this->nested_url_parenthesis_re = 
            str_repeat('(?>[^()\s]+|\(', $this->nested_url_parenthesis_depth).
            str_repeat('(?>\)))*', $this->nested_url_parenthesis_depth);
        
        $this->escape_chars_re = '['.preg_quote($this->escape_chars).']';
        
        # Sort document, block, and span gamut in ascendent priority order.
        asort($this->document_gamut);
        asort($this->block_gamut);
        asort($this->span_gamut);
    }


    # Internal hashes used during transformation.
    protected $urls = array();
    protected $titles = array();
    protected $html_hashes = array();
    
    # Status flag to avoid invalid nesting.
    protected $in_anchor = false;
    
    
    protected function setup() {
    #
    # Called before the transformation process starts to setup parser 
    # states.
    #
        # Clear global hashes.
        $this->urls = $this->predef_urls;
        $this->titles = $this->predef_titles;
        $this->html_hashes = array();
        
        $this->in_anchor = false;
    }
    
    protected function teardown() {
    #
    # Called after the transformation process to clear any variable 
    # which may be taking up memory unnecessarly.
    #
        $this->urls = array();
        $this->titles = array();
        $this->html_hashes = array();
    }


    public function transform($text) {
    #
    # Main function. Performs some preprocessing on the input text
    # and pass it through the document gamut.
    #
        $this->setup();
    
        # Remove UTF-8 BOM and marker character in input, if present.
        $text = preg_replace('{^\xEF\xBB\xBF|\x1A}', '', $text);

        # Standardize line endings:
        #   DOS to Unix and Mac to Unix
        $text = preg_replace('{\r\n?}', "\n", $text);

        # Make sure $text ends with a couple of newlines:
        $text .= "\n\n";

        # Convert all tabs to spaces.
        $text = $this->detab($text);

        # Turn block-level HTML blocks into hash entries
        $text = $this->hashHTMLBlocks($text);

        # Strip any lines consisting only of spaces and tabs.
        # This makes subsequent regexen easier to write, because we can
        # match consecutive blank lines with /\n+/ instead of something
        # contorted like /[ ]*\n+/ .
        $text = preg_replace('/^[ ]+$/m', '', $text);

        # Run document gamut methods.
        foreach ($this->document_gamut as $method => $priority) {
            $text = $this->$method($text);
        }
        
        $this->teardown();

        $text = preg_replace_callback("/<\/?(\!doctype|html|head|body|link|title|input|select|button|textarea|style|noscript)[^>]*>/is", 
            array($this, '_doEscape_callback'), $text);

        return $text . "\n";
    }

    /**
     * _doEscape_callback  
     * 
     * @param array $matches 
     * @access protected
     * @return string
     */
    protected function _doEscape_callback($matches) {
        return htmlspecialchars($matches[0], ENT_NOQUOTES);
    }
    
    protected $document_gamut = array(
        # Strip link definitions, store in hashes.
        "stripLinkDefinitions" => 20,
        
        "runBasicBlockGamut"   => 30,
        );


    protected function stripLinkDefinitions($text) {
    #
    # Strips link definitions from text, stores the URLs and titles in
    # hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: ^[id]: url "optional title"
        $text = preg_replace_callback('{
                            ^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?: # id = $1
                              [ ]*
                              \n?               # maybe *one* newline
                              [ ]*
                            (?:
                              <(.+?)>           # url = $2
                            |
                              (\S+?)            # url = $3
                            )
                              [ ]*
                              \n?               # maybe one newline
                              [ ]*
                            (?:
                                (?<=\s)         # lookbehind for whitespace
                                ["(]
                                (.*?)           # title = $4
                                [")]
                                [ ]*
                            )?  # title is optional
                            (?:\n+|\Z)
            }xm',
            array($this, '_stripLinkDefinitions_callback'),
            $text);
        return $text;
    }
    protected function _stripLinkDefinitions_callback($matches) {
        $link_id = strtolower($matches[1]);
        $url = $matches[2] == '' ? $matches[3] : $matches[2];
        $this->urls[$link_id] = $url;
        $this->titles[$link_id] =& $matches[4];
        return ''; # String that will replace the block
    }


    protected function hashHTMLBlocks($text) {
        if ($this->no_markup)  return $text;

        $less_than_tab = $this->tab_width - 1;

        # Hashify HTML blocks:
        # We only want to do this for block-level HTML tags, such as headers,
        # lists, and tables. That's because we still want to wrap <p>s around
        # "paragraphs" that are wrapped in non-block-level tags, such as anchors,
        # phrase emphasis, and spans. The list of tags we're looking for is
        # hard-coded:
        #
        # *  List "a" is made of tags which can be both inline or block-level.
        #    These will be treated block-level when the start tag is alone on 
        #    its line, otherwise they're not matched here and will be taken as 
        #    inline later.
        # *  List "b" is made of tags which are always block-level;
        #
        $block_tags_a_re = 'ins|del';
        $block_tags_b_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|'.
                           'script|noscript|form|fieldset|iframe|math|svg|'.
                           'article|section|nav|aside|hgroup|header|footer|'.
                           'figure';

        # Regular expression for the content of a block tag.
        $nested_tags_level = 4;
        $attr = '
            (?>             # optional tag attributes
              \s            # starts with whitespace
              (?>
                [^>"/]+     # text outside quotes
              |
                /+(?!>)     # slash not followed by ">"
              |
                "[^"]*"     # text inside double quotes (tolerate ">")
              |
                \'[^\']*\'  # text inside single quotes (tolerate ">")
              )*
            )?  
            ';
        $content =
            str_repeat('
                (?>
                  [^<]+         # content without tag
                |
                  <\2           # nested opening tag
                    '.$attr.'   # attributes
                    (?>
                      />
                    |
                      >', $nested_tags_level).  # end of opening tag
                      '.*?'.                    # last level nested tag content
            str_repeat('
                      </\2\s*>  # closing nested tag
                    )
                  |             
                    <(?!/\2\s*> # other tags with a different name
                  )
                )*',
                $nested_tags_level);
        $content2 = str_replace('\2', '\3', $content);

        # First, look for nested blocks, e.g.:
        #   <div>
        #       <div>
        #       tags for inner block must be indented.
        #       </div>
        #   </div>
        #
        # The outermost tags must start at the left margin for this to match, and
        # the inner nested divs must be indented.
        # We need to do this before the next, more liberal match, because the next
        # match will start at the first `<div>` and stop at the first `</div>`.
        $text = preg_replace_callback('{(?>
            (?>
                (?<=\n\n)       # Starting after a blank line
                |               # or
                \A\n?           # the beginning of the doc
            )
            (                       # save in $1

              # Match from `\n<tag>` to `</tag>\n`, handling nested tags 
              # in between.
                    
                        [ ]{0,'.$less_than_tab.'}
                        <('.$block_tags_b_re.')# start tag = $2
                        '.$attr.'>          # attributes followed by > and \n
                        '.$content.'        # content, support nesting
                        </\2>               # the matching end tag
                        [ ]*                # trailing spaces/tabs
                        (?=\n+|\Z)  # followed by a newline or end of document

            | # Special version for tags of group a.

                        [ ]{0,'.$less_than_tab.'}
                        <('.$block_tags_a_re.')# start tag = $3
                        '.$attr.'>[ ]*\n    # attributes followed by >
                        '.$content2.'       # content, support nesting
                        </\3>               # the matching end tag
                        [ ]*                # trailing spaces/tabs
                        (?=\n+|\Z)  # followed by a newline or end of document
                    
            | # Special case just for <hr />. It was easier to make a special 
              # case than to make the other regex more complicated.
            
                        [ ]{0,'.$less_than_tab.'}
                        <(hr)               # start tag = $2
                        '.$attr.'           # attributes
                        /?>                 # the matching end tag
                        [ ]*
                        (?=\n{2,}|\Z)       # followed by a blank line or end of document
            
            | # Special case for standalone HTML comments:
            
                    [ ]{0,'.$less_than_tab.'}
                    (?s:
                        <!-- .*? -->
                    )
                    [ ]*
                    (?=\n{2,}|\Z)       # followed by a blank line or end of document
            
            | # PHP and ASP-style processor instructions (<? and <%)
            
                    [ ]{0,'.$less_than_tab.'}
                    (?s:
                        <([?%])         # $2
                        .*?
                        \2>
                    )
                    [ ]*
                    (?=\n{2,}|\Z)       # followed by a blank line or end of document
                    
            )
            )}Sxmi',
            array($this, '_hashHTMLBlocks_callback'),
            $text);

        return $text;
    }
    protected function _hashHTMLBlocks_callback($matches) {
        $text = $matches[1];
        return $this->hashBlock($text);
        // return "\n\n$key\n\n";
    }
    
    
    protected function hashPart($text, $boundary = 'X') {
    #
    # Called whenever a tag must be hashed when a function insert an atomic 
    # element in the text stream. Passing $text to through this function gives
    # a unique text-token which will be reverted back when calling unhash.
    #
    # The $boundary argument specify what character should be used to surround
    # the token. By convension, "B" is used for block elements that needs not
    # to be wrapped into paragraph tags at the end, ":" is used for elements
    # that are word separators and "X" is used in the general case.
    #
        # Swap back any tag hash found in $text so we do not have to `unhash`
        # multiple times at the end.
        $text = $this->unhash($text);
        
        # Then hash the block.
        static $i = 0;
        $key = "$boundary\x1A" . ++$i . $boundary;
        $this->html_hashes[$key] = $text;
        return $key; # String that will replace the tag.
    }


    protected function hashBlock($text) {
    #
    # Shortcut function for hashPart with block-level boundaries.
    #
        return $this->hashPart($text, 'B');
    }


    protected $block_gamut = array(
    #
    # These are all the transformations that form block-level
    # tags like paragraphs, headers, and list items.
    #
        "doHeaders"         => 10,
        "doHorizontalRules" => 20,
        
        "doLists"           => 40,
        "doCodeBlocks"      => 50,
        "doBlockQuotes"     => 60,
        );

    protected function runBlockGamut($text) {
    #
    # Run block gamut tranformations.
    #
        # We need to escape raw HTML in Markdown source before doing anything 
        # else. This need to be done for each block, and not only at the 
        # begining in the Markdown function since hashed blocks can be part of
        # list items and could have been indented. Indented blocks would have 
        # been seen as a code block in a previous pass of hashHTMLBlocks.
        $text = $this->hashHTMLBlocks($text);
        
        return $this->runBasicBlockGamut($text);
    }
    
    protected function runBasicBlockGamut($text) {
    #
    # Run block gamut tranformations, without hashing HTML blocks. This is 
    # useful when HTML blocks are known to be already hashed, like in the first
    # whole-document pass.
    #
        foreach ($this->block_gamut as $method => $priority) {
            $text = $this->$method($text);
        }
        
        # Finally form paragraph and restore hashed blocks.
        $text = $this->formParagraphs($text);

        return $text;
    }
    
    
    protected function doHorizontalRules($text) {
        # Do Horizontal Rules:
        return preg_replace(
            '{
                ^[ ]{0,3}   # Leading space
                ([-*_])     # $1: First marker
                (?>         # Repeated marker group
                    [ ]{0,2}    # Zero, one, or two spaces.
                    \1          # Marker character
                ){2,}       # Group repeated at least twice
                [ ]*        # Tailing spaces
                $           # End of line.
            }mx',
            "\n".$this->hashBlock("<hr$this->empty_element_suffix")."\n", 
            $text);
    }


    protected $span_gamut = array(
    #
    # These are all the transformations that occur *within* block-level
    # tags like paragraphs, headers, and list items.
    #
        # Process character escapes, code spans, and inline HTML
        # in one shot.
        "parseSpan"           => -30,

        # Process anchor and image tags. Images must come first,
        # because ![foo][f] looks like an anchor.
        "doImages"            =>  10,
        "doAnchors"           =>  20,
        
        # Make links out of things like `<http://example.com/>`
        # Must come after doAnchors, because you can use < and >
        # delimiters in inline links like [this](<url>).
        "doAutoLinks"         =>  30,
        "encodeAmpsAndAngles" =>  40,

        "doItalicsAndBold"    =>  50,
        "doHardBreaks"        =>  60,
        );

    protected function runSpanGamut($text) {
    #
    # Run span gamut tranformations.
    #
        foreach ($this->span_gamut as $method => $priority) {
            $text = $this->$method($text);
        }

        return $text;
    }
    
    
    protected function doHardBreaks($text) {
        # Do hard breaks:
        return preg_replace_callback('/ {2,}\n/', 
            array($this, '_doHardBreaks_callback'), $text);
    }
    protected function _doHardBreaks_callback($matches) {
        return $this->hashPart("<br$this->empty_element_suffix\n");
    }


    protected function doAnchors($text) {
    #
    # Turn Markdown link shortcuts into XHTML <a> tags.
    #
        if ($this->in_anchor) return $text;
        $this->in_anchor = true;
        
        #
        # First, handle reference-style links: [link text] [id]
        #
        $text = preg_replace_callback('{
            (                   # wrap whole match in $1
              \[
                ('.$this->nested_brackets_re.') # link text = $2
              \]

              [ ]?              # one optional space
              (?:\n[ ]*)?       # one optional newline followed by spaces

              \[
                (.*?)       # id = $3
              \]
            )
            }xs',
            array($this, '_doAnchors_reference_callback'), $text);

        #
        # Next, inline-style links: [link text](url "optional title")
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              \[
                ('.$this->nested_brackets_re.') # link text = $2
              \]
              \(            # literal paren
                [ \n]*
                (?:
                    <(.+?)> # href = $3
                |
                    ('.$this->nested_url_parenthesis_re.')  # href = $4
                )
                [ \n]*
                (           # $5
                  ([\'"])   # quote char = $6
                  (.*?)     # Title = $7
                  \6        # matching quote
                  [ \n]*    # ignore any spaces/tabs between closing quote and )
                )?          # title is optional
              \)
            )
            }xs',
            array($this, '_doAnchors_inline_callback'), $text);

        #
        # Last, handle reference-style shortcuts: [link text]
        # These must come last in case you've also got [link text][1]
        # or [link text](/foo)
        #
        $text = preg_replace_callback('{
            (                   # wrap whole match in $1
              \[
                ([^\[\]]+)      # link text = $2; can\'t contain [ or ]
              \]
            )
            }xs',
            array($this, '_doAnchors_reference_callback'), $text);

        $this->in_anchor = false;
        return $text;
    }
    protected function _doAnchors_reference_callback($matches) {
        $whole_match =  $matches[1];
        $link_text   =  $matches[2];
        $link_id     =& $matches[3];

        if ($link_id == "") {
            # for shortcut links like [this][] or [this].
            $link_id = $link_text;
        }
        
        # lower-case and turn embedded newlines into spaces
        $link_id = strtolower($link_id);
        $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

        if (isset($this->urls[$link_id])) {
            $url = $this->urls[$link_id];
            $url = $this->encodeAttribute($url);
            
            $result = "<a href=\"$url\"";
            if ( isset( $this->titles[$link_id] ) ) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
        
            $link_text = $this->runSpanGamut($link_text);
            $result .= ">$link_text</a>";
            $result = $this->hashPart($result);
        }
        else {
            $result = $whole_match;
        }
        return $result;
    }
    protected function _doAnchors_inline_callback($matches) {
        $whole_match    =  $matches[1];
        $link_text      =  $this->runSpanGamut($matches[2]);
        $url            =  $matches[3] == '' ? $matches[4] : $matches[3];
        $title          =& $matches[7];

        $url = $this->encodeAttribute($url);

        $result = "<a href=\"$url\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\"";
        }
        
        $link_text = $this->runSpanGamut($link_text);
        $result .= ">$link_text</a>";

        return $this->hashPart($result);
    }


    protected function doImages($text) {
    #
    # Turn Markdown image shortcuts into <img> tags.
    #
        #
        # First, handle reference-style labeled images: ![alt text][id]
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              !\[
                ('.$this->nested_brackets_re.')     # alt text = $2
              \]

              [ ]?              # one optional space
              (?:\n[ ]*)?       # one optional newline followed by spaces

              \[
                (.*?)       # id = $3
              \]

            )
            }xs', 
            array($this, '_doImages_reference_callback'), $text);

        #
        # Next, handle inline images:  ![alt text](url "optional title")
        # Don't forget: encode * and _
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              !\[
                ('.$this->nested_brackets_re.')     # alt text = $2
              \]
              \s?           # One optional whitespace character
              \(            # literal paren
                [ \n]*
                (?:
                    <(\S*)> # src url = $3
                |
                    ('.$this->nested_url_parenthesis_re.')  # src url = $4
                )
                [ \n]*
                (           # $5
                  ([\'"])   # quote char = $6
                  (.*?)     # title = $7
                  \6        # matching quote
                  [ \n]*
                )?          # title is optional
              \)
            )
            }xs',
            array($this, '_doImages_inline_callback'), $text);

        return $text;
    }
    protected function _doImages_reference_callback($matches) {
        $whole_match = $matches[1];
        $alt_text    = $matches[2];
        $link_id     = strtolower($matches[3]);

        if ($link_id == "") {
            $link_id = strtolower($alt_text); # for shortcut links like ![this][].
        }

        $alt_text = $this->encodeAttribute($alt_text);
        if (isset($this->urls[$link_id])) {
            $url = $this->encodeAttribute($this->urls[$link_id]);
            $result = "<img src=\"$url\" alt=\"$alt_text\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
            $result .= $this->empty_element_suffix;
            $result = $this->hashPart($result);
        }
        else {
            # If there's no such link ID, leave intact:
            $result = $whole_match;
        }

        return $result;
    }
    protected function _doImages_inline_callback($matches) {
        $whole_match    = $matches[1];
        $alt_text       = $matches[2];
        $url            = $matches[3] == '' ? $matches[4] : $matches[3];
        $title          =& $matches[7];

        $alt_text = $this->encodeAttribute($alt_text);
        $url = $this->encodeAttribute($url);
        $result = "<img src=\"$url\" alt=\"$alt_text\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\""; # $title already quoted
        }
        $result .= $this->empty_element_suffix;

        return $this->hashPart($result);
    }


    protected function doHeaders($text) {
        # Setext-style headers:
        #     Header 1
        #     ========
        #  
        #     Header 2
        #     --------
        #
        $text = preg_replace_callback('{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
            array($this, '_doHeaders_callback_setext'), $text);

        # atx-style headers:
        #   # Header 1
        #   ## Header 2
        #   ## Header 2 with closing hashes ##
        #   ...
        #   ###### Header 6
        #
        $text = preg_replace_callback('{
                ^(\#{1,6})  # $1 = string of #\'s
                [ ]*
                (.+?)       # $2 = Header text
                [ ]*
                \#*         # optional closing #\'s (not counted)
                \n+
            }xm',
            array($this, '_doHeaders_callback_atx'), $text);

        return $text;
    }
    protected function _doHeaders_callback_setext($matches) {
        # Terrible hack to check we haven't found an empty list item.
        if ($matches[2] == '-' && preg_match('{^-(?: |$)}', $matches[1]))
            return $matches[0];
        
        $level = $matches[2]{0} == '=' ? 1 : 2;
        $block = "<h$level>".$this->runSpanGamut($matches[1])."</h$level>";
        return "\n" . $this->hashBlock($block) . "\n\n";
    }
    protected function _doHeaders_callback_atx($matches) {
        $level = strlen($matches[1]);
        $block = "<h$level>".$this->runSpanGamut($matches[2])."</h$level>";
        return "\n" . $this->hashBlock($block) . "\n\n";
    }


    protected function doLists($text) {
    #
    # Form HTML ordered (numbered) and unordered (bulleted) lists.
    #
        $less_than_tab = $this->tab_width - 1;

        # Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re  = '[*+-]';
        $marker_ol_re  = '\d+[\.]';
        $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

        $markers_relist = array(
            $marker_ul_re => $marker_ol_re,
            $marker_ol_re => $marker_ul_re,
            );

        foreach ($markers_relist as $marker_re => $other_marker_re) {
            # Re-usable pattern to match any entirel ul or ol list:
            $whole_list_re = '
                (                               # $1 = whole list
                  (                             # $2
                    ([ ]{0,'.$less_than_tab.'}) # $3 = number of spaces
                    ('.$marker_re.')            # $4 = first list item marker
                    [ ]+
                  )
                  (?s:.+?)
                  (                             # $5
                      \z
                    |
                      \n{2,}
                      (?=\S)
                      (?!                       # Negative lookahead for another list item marker
                        [ ]*
                        '.$marker_re.'[ ]+
                      )
                    |
                      (?=                       # Lookahead for another kind of list
                        \n
                        \3                      # Must have the same indentation
                        '.$other_marker_re.'[ ]+
                      )
                  )
                )
            '; // mx
            
            # We use a different prefix before nested lists than top-level lists.
            # See extended comment in _ProcessListItems().
        
            if ($this->list_level) {
                $text = preg_replace_callback('{
                        ^
                        '.$whole_list_re.'
                    }mx',
                    array($this, '_doLists_callback'), $text);
            }
            else {
                $text = preg_replace_callback('{
                        (?:(?<=\n)\n?|\A\n?) # Must eat the newline
                        '.$whole_list_re.'
                    }mx',
                    array($this, '_doLists_callback'), $text);
            }
        }

        return $text;
    }
    protected function _doLists_callback($matches) {
        # Re-usable patterns to match list item bullets and number markers:
        $marker_ul_re  = '[*+-]';
        $marker_ol_re  = '\d+[\.]';
        $marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";
        
        $list = $matches[1];
        $list_type = preg_match("/$marker_ul_re/", $matches[4]) ? "ul" : "ol";
        
        $marker_any_re = ( $list_type == "ul" ? $marker_ul_re : $marker_ol_re );
        
        $list .= "\n";
        $result = $this->processListItems($list, $marker_any_re);
        
        $result = $this->hashBlock("<$list_type>\n" . $result . "</$list_type>");
        return "\n". $result ."\n\n";
    }

    protected $list_level = 0;

    protected function processListItems($list_str, $marker_any_re) {
    #
    #   Process the contents of a single ordered or unordered list, splitting it
    #   into individual list items.
    #
        # The $this->list_level global keeps track of when we're inside a list.
        # Each time we enter a list, we increment it; when we leave a list,
        # we decrement. If it's zero, we're not in a list anymore.
        #
        # We do this because when we're not inside a list, we want to treat
        # something like this:
        #
        #       I recommend upgrading to version
        #       8. Oops, now this line is treated
        #       as a sub-list.
        #
        # As a single paragraph, despite the fact that the second line starts
        # with a digit-period-space sequence.
        #
        # Whereas when we're inside a list (or sub-list), that line will be
        # treated as the start of a sub-list. What a kludge, huh? This is
        # an aspect of Markdown's syntax that's hard to parse perfectly
        # without resorting to mind-reading. Perhaps the solution is to
        # change the syntax rules such that sub-lists must start with a
        # starting cardinal number; e.g. "1." or "a.".
        
        $this->list_level++;

        # trim trailing blank lines:
        $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

        $list_str = preg_replace_callback('{
            (\n)?                           # leading line = $1
            (^[ ]*)                         # leading whitespace = $2
            ('.$marker_any_re.'             # list marker and space = $3
                (?:[ ]+|(?=\n)) # space only required if item is not empty
            )
            ((?s:.*?))                      # list item text   = $4
            (?:(\n+(?=\n))|\n)              # tailing blank line = $5
            (?= \n* (\z | \2 ('.$marker_any_re.') (?:[ ]+|(?=\n))))
            }xm',
            array($this, '_processListItems_callback'), $list_str);

        $this->list_level--;
        return $list_str;
    }
    protected function _processListItems_callback($matches) {
        $item = $matches[4];
        $leading_line =& $matches[1];
        $leading_space =& $matches[2];
        $marker_space = $matches[3];
        $tailing_blank_line =& $matches[5];

        if ($leading_line || $tailing_blank_line || 
            preg_match('/\n{2,}/', $item))
        {
            # Replace marker with the appropriate whitespace indentation
            $item = $leading_space . str_repeat(' ', strlen($marker_space)) . $item;
            $item = $this->runBlockGamut($this->outdent($item)."\n");
        }
        else {
            # Recursion for sub-lists:
            $item = $this->doLists($this->outdent($item));
            $item = preg_replace('/\n+$/', '', $item);
            $item = $this->runSpanGamut($item);
        }

        return "<li>" . $item . "</li>\n";
    }


    protected function doCodeBlocks($text) {
    #
    #   Process Markdown `<pre><code>` blocks.
    #
        $text = preg_replace_callback('{
                (?:\n\n|\A\n?)
                (               # $1 = the code block -- one or more lines, starting with a space/tab
                  (?>
                    [ ]{'.$this->tab_width.'}  # Lines must start with a tab or a tab-width of spaces
                    .*\n+
                  )+
                )
                ((?=^[ ]{0,'.$this->tab_width.'}\S)|\Z) # Lookahead for non-space at line-start, or end of doc
            }xm',
            array($this, '_doCodeBlocks_callback'), $text);

        return $text;
    }
    protected function _doCodeBlocks_callback($matches) {
        $codeblock = $this->unhash($matches[1]);

        $codeblock = $this->outdent($codeblock);
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);

        # trim leading newlines and trailing newlines
        $codeblock = preg_replace('/\A\n+|\n+\z/', '', $codeblock);

        $codeblock = "<pre><code>$codeblock\n</code></pre>";
        return "\n\n".$this->hashBlock($codeblock)."\n\n";
    }


    protected function makeCodeSpan($code) {
    #
    # Create a code span markup for $code. Called from handleSpanToken.
    #
        $code = htmlspecialchars(trim($code), ENT_NOQUOTES);
        return $this->hashPart("<code>$code</code>");
    }


    protected $em_relist = array(
        ''  => '(?:(?<!\*)\*(?!\*)|(?<!_)_(?!_))(?=\S|$)(?![\.,:;]\s)',
        '*' => '(?<=\S|^)(?<!\*)\*(?!\*)',
        '_' => '(?<=\S|^)(?<!_)_(?!_)',
        );
    protected $strong_relist = array(
        ''   => '(?:(?<!\*)\*\*(?!\*)|(?<!_)__(?!_))(?=\S|$)(?![\.,:;]\s)',
        '**' => '(?<=\S|^)(?<!\*)\*\*(?!\*)',
        '__' => '(?<=\S|^)(?<!_)__(?!_)',
        );
    protected $em_strong_relist = array(
        ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<!_)___(?!_))(?=\S|$)(?![\.,:;]\s)',
        '***' => '(?<=\S|^)(?<!\*)\*\*\*(?!\*)',
        '___' => '(?<=\S|^)(?<!_)___(?!_)',
        );
    protected $em_strong_prepared_relist;
    
    protected function prepareItalicsAndBold() {
    #
    # Prepare regular expressions for searching emphasis tokens in any
    # context.
    #
        foreach ($this->em_relist as $em => $em_re) {
            foreach ($this->strong_relist as $strong => $strong_re) {
                # Construct list of allowed token expressions.
                $token_relist = array();
                if (isset($this->em_strong_relist["$em$strong"])) {
                    $token_relist[] = $this->em_strong_relist["$em$strong"];
                }
                $token_relist[] = $em_re;
                $token_relist[] = $strong_re;
                
                # Construct master expression from list.
                $token_re = '{('. implode('|', $token_relist) .')}';
                $this->em_strong_prepared_relist["$em$strong"] = $token_re;
            }
        }
    }
    
    protected function doItalicsAndBold($text) {
        $token_stack = array('');
        $text_stack = array('');
        $em = '';
        $strong = '';
        $tree_char_em = false;
        
        while (1) {
            #
            # Get prepared regular expression for seraching emphasis tokens
            # in current context.
            #
            $token_re = $this->em_strong_prepared_relist["$em$strong"];
            
            #
            # Each loop iteration search for the next emphasis token. 
            # Each token is then passed to handleSpanToken.
            #
            $parts = preg_split($token_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
            $text_stack[0] .= $parts[0];
            $token =& $parts[1];
            $text =& $parts[2];
            
            if (empty($token)) {
                # Reached end of text span: empty stack without emitting.
                # any more emphasis.
                while ($token_stack[0]) {
                    $text_stack[1] .= array_shift($token_stack);
                    $text_stack[0] .= array_shift($text_stack);
                }
                break;
            }
            
            $token_len = strlen($token);
            if ($tree_char_em) {
                # Reached closing marker while inside a three-char emphasis.
                if ($token_len == 3) {
                    # Three-char closing marker, close em and strong.
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong><em>$span</em></strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $em = '';
                    $strong = '';
                } else {
                    # Other closing marker: close one em or strong and
                    # change current token state to match the other
                    $token_stack[0] = str_repeat($token{0}, 3-$token_len);
                    $tag = $token_len == 2 ? "strong" : "em";
                    $span = $text_stack[0];
                    $span = $this->runSpanGamut($span);
                    $span = "<$tag>$span</$tag>";
                    $text_stack[0] = $this->hashPart($span);
                    $$tag = ''; # $$tag stands for $em or $strong
                }
                $tree_char_em = false;
            } else if ($token_len == 3) {
                if ($em) {
                    # Reached closing marker for both em and strong.
                    # Closing strong marker:
                    for ($i = 0; $i < 2; ++$i) {
                        $shifted_token = array_shift($token_stack);
                        $tag = strlen($shifted_token) == 2 ? "strong" : "em";
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<$tag>$span</$tag>";
                        $text_stack[0] .= $this->hashPart($span);
                        $$tag = ''; # $$tag stands for $em or $strong
                    }
                } else {
                    # Reached opening three-char emphasis marker. Push on token 
                    # stack; will be handled by the special condition above.
                    $em = $token{0};
                    $strong = "$em$em";
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $tree_char_em = true;
                }
            } else if ($token_len == 2) {
                if ($strong) {
                    # Unwind any dangling emphasis marker:
                    if (strlen($token_stack[0]) == 1) {
                        $text_stack[1] .= array_shift($token_stack);
                        $text_stack[0] .= array_shift($text_stack);
                    }
                    # Closing strong marker:
                    array_shift($token_stack);
                    $span = array_shift($text_stack);
                    $span = $this->runSpanGamut($span);
                    $span = "<strong>$span</strong>";
                    $text_stack[0] .= $this->hashPart($span);
                    $strong = '';
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $strong = $token;
                }
            } else {
                # Here $token_len == 1
                if ($em) {
                    if (strlen($token_stack[0]) == 1) {
                        # Closing emphasis marker:
                        array_shift($token_stack);
                        $span = array_shift($text_stack);
                        $span = $this->runSpanGamut($span);
                        $span = "<em>$span</em>";
                        $text_stack[0] .= $this->hashPart($span);
                        $em = '';
                    } else {
                        $text_stack[0] .= $token;
                    }
                } else {
                    array_unshift($token_stack, $token);
                    array_unshift($text_stack, '');
                    $em = $token;
                }
            }
        }
        return $text_stack[0];
    }


    protected function doBlockQuotes($text) {
        $text = preg_replace_callback('/
              (                             # Wrap whole match in $1
                (?>
                  ^[ ]*>[ ]?            # ">" at the start of a line
                    .+\n                    # rest of the first line
                  (.+\n)*                   # subsequent consecutive lines
                  \n*                       # blanks
                )+
              )
            /xm',
            array($this, '_doBlockQuotes_callback'), $text);

        return $text;
    }
    protected function _doBlockQuotes_callback($matches) {
        $bq = $matches[1];
        # trim one level of quoting - trim whitespace-only lines
        $bq = preg_replace('/^[ ]*>[ ]?|^[ ]+$/m', '', $bq);
        $bq = $this->runBlockGamut($bq);        # recurse

        $bq = preg_replace('/^/m', "  ", $bq);
        # These leading spaces cause problem with <pre> content, 
        # so we need to fix that:
        $bq = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx', 
            array($this, '_doBlockQuotes_callback2'), $bq);

        return "\n". $this->hashBlock("<blockquote>\n$bq\n</blockquote>")."\n\n";
    }
    protected function _doBlockQuotes_callback2($matches) {
        $pre = $matches[1];
        $pre = preg_replace('/^  /m', '', $pre);
        return $pre;
    }


    protected function formParagraphs($text) {
    #
    #   Params:
    #       $text - string to process with html <p> tags
    #
        # Strip leading and trailing lines:
        $text = preg_replace('/\A\n+|\n+\z/', '', $text);

        $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

        #
        # Wrap <p> tags and unhashify HTML blocks
        #
        foreach ($grafs as $key => $value) {
            if (!preg_match('/^B\x1A[0-9]+B$/', $value)) {
                # Is a paragraph.
                $value = $this->runSpanGamut($value);
                $value = preg_replace('/^([ ]*)/', "<p>", $value);
                $value .= "</p>";
                $grafs[$key] = $this->unhash($value);
            }
            else {
                # Is a block.
                # Modify elements of @grafs in-place...
                $graf = $value;
                $block = $this->html_hashes[$graf];
                $graf = $block;
//              if (preg_match('{
//                  \A
//                  (                           # $1 = <div> tag
//                    <div  \s+
//                    [^>]*
//                    \b
//                    markdown\s*=\s*  ([\'"])  #   $2 = attr quote char
//                    1
//                    \2
//                    [^>]*
//                    >
//                  )
//                  (                           # $3 = contents
//                  .*
//                  )
//                  (</div>)                    # $4 = closing tag
//                  \z
//                  }xs', $block, $matches))
//              {
//                  list(, $div_open, , $div_content, $div_close) = $matches;
//
//                  # We can't call Markdown(), because that resets the hash;
//                  # that initialization code should be pulled into its own sub, though.
//                  $div_content = $this->hashHTMLBlocks($div_content);
//                  
//                  # Run document gamut methods on the content.
//                  foreach ($this->document_gamut as $method => $priority) {
//                      $div_content = $this->$method($div_content);
//                  }
//
//                  $div_open = preg_replace(
//                      '{\smarkdown\s*=\s*([\'"]).+?\1}', '', $div_open);
//
//                  $graf = $div_open . "\n" . $div_content . "\n" . $div_close;
//              }
                $grafs[$key] = $graf;
            }
        }

        return implode("\n\n", $grafs);
    }


    protected function encodeAttribute($text) {
    #
    # Encode text for a double-quoted HTML attribute. This function
    # is *not* suitable for attributes enclosed in single quotes.
    #
        $text = $this->encodeAmpsAndAngles($text);
        $text = str_replace('"', '&quot;', $text);
        return $text;
    }
    
    
    protected function encodeAmpsAndAngles($text) {
    #
    # Smart processing for ampersands and angle brackets that need to 
    # be encoded. Valid character entities are left alone unless the
    # no-entities mode is set.
    #
        if ($this->no_entities) {
            $text = str_replace('&', '&amp;', $text);
        } else {
            # Ampersand-encoding based entirely on Nat Irons's Amputator
            # MT plugin: <http://bumppo.net/projects/amputator/>
            $text = preg_replace('/&(?!#?[xX]?(?:[0-9a-fA-F]+|\w+);)/', 
                                '&amp;', $text);;
        }
        # Encode remaining <'s
        $text = str_replace('<', '&lt;', $text);

        return $text;
    }


    protected function doAutoLinks($text) {
        $text = preg_replace_callback('/(="|<)?\b(https?|ftp)(:\/\/[-A-Z0-9+&@#\/%?=~_|\[\]\(\)!:,\.;]*[-A-Z0-9+&@#\/%=~_|\[\])])(?=$|\W)/i', 
            array($this, '_doAutoLinks_url_callback'), $text);
        $text = preg_replace_callback('{<((https?|ftp|dict):[^\'">\s]+)>}i', 
            array($this, '_doAutoLinks_url_callback_replace'), $text);

        # Email addresses: <address@domain.foo>
        $text = preg_replace_callback('{
            <
            (?:mailto:)?
            (
                (?:
                    [-!#$%&\'*+/=?^_`.{|}~\w\x80-\xFF]+
                |
                    ".*?"
                )
                \@
                (?:
                    [-a-z0-9\x80-\xFF]+(\.[-a-z0-9\x80-\xFF]+)*\.[a-z]+
                |
                    \[[\d.a-fA-F:]+\]   # IPv4 & IPv6
                )
            )
            >
            }xi',
            array($this, '_doAutoLinks_email_callback'), $text);

        return $text;
    }
    protected function _doAutoLinks_url_callback_replace($matches) {
        $url = $this->encodeAttribute($matches[1]);
        $link = "<a href=\"$url\">$url</a>";
        return $this->hashPart($link);
    }

    private $tail;

    protected function _doAutoLinks_url_callback($matches) {
        list ($wholeMatch, $lookbehind, $protocol, $link) = $matches;

        if ($lookbehind) {
            return $wholeMatch;
        }

        if ($link[strlen($link) - 1] != ')') {
            return '<' . $protocol . $link . '>';
        }

        $level = 0;
        if (preg_match_all("/[()]/", $link, $matches)) {
            foreach ($matches[0] as $op) {
                if ('(' == $op) {
                    if ($level <= 0) {
                        $level = 1;
                    } else {
                        $level ++;
                    }
                } else {
                    $level --;
                }
            }
        }

        $this->tail = '';
        if ($level < 0) {
            $link = preg_replace_callback("/\){1," . (- $level) . "}$/", 
                array($this, '_doAutoLinks_url_callback_callback'), $link);
        }

        $url = $this->encodeAttribute($protocol . $link);
        $link = "<a href=\"$url\">$url</a>";
        return $this->hashPart($link) . $this->tail;
    }

    protected function _doAutoLinks_email_callback($matches) {
        $address = $matches[1];
        $link = $this->encodeEmailAddress($address);
        return $this->hashPart($link);
    }

    protected function _doAutoLinks_url_callback_callback($matches) {
        $this->tail = $matches[0];
        return '';
    }

    protected function encodeEmailAddress($addr) {
    #
    #   Input: an email address, e.g. "foo@example.com"
    #
    #   Output: the email address as a mailto link, with each character
    #       of the address encoded as either a decimal or hex entity, in
    #       the hopes of foiling most address harvesting spam bots. E.g.:
    #
    #     <p><a href="&#109;&#x61;&#105;&#x6c;&#116;&#x6f;&#58;&#x66;o&#111;
    #        &#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;&#101;&#46;&#x63;&#111;
    #        &#x6d;">&#x66;o&#111;&#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;
    #        &#101;&#46;&#x63;&#111;&#x6d;</a></p>
    #
    #   Based by a filter by Matthew Wickline, posted to BBEdit-Talk.
    #   With some optimizations by Milian Wolff.
    #
        $addr = "mailto:" . $addr;
        $chars = preg_split('/(?<!^)(?!$)/', $addr);
        $seed = (int)abs(crc32($addr) / strlen($addr)); # Deterministic seed.
        
        foreach ($chars as $key => $char) {
            $ord = ord($char);
            # Ignore non-ascii chars.
            if ($ord < 128) {
                $r = ($seed * (1 + $key)) % 100; # Pseudo-random function.
                # roughly 10% raw, 45% hex, 45% dec
                # '@' *must* be encoded. I insist.
                if ($r > 90 && $char != '@') /* do nothing */;
                else if ($r < 45) $chars[$key] = '&#x'.dechex($ord).';';
                else              $chars[$key] = '&#'.$ord.';';
            }
        }
        
        $addr = implode('', $chars);
        $text = implode('', array_slice($chars, 7)); # text without `mailto:`
        $addr = "<a href=\"$addr\">$text</a>";

        return $addr;
    }


    protected function parseSpan($str) {
    #
    # Take the string $str and parse it into tokens, hashing embeded HTML,
    # escaped characters and handling code spans.
    #
        $output = '';
        
        $span_re = '{
                (
                    \\\\'.$this->escape_chars_re.'
                |
                    (?<![`\\\\])
                    `+                      # code span marker
            '.( $this->no_markup ? '' : '
                |
                    <!--    .*?     -->     # comment
                |
                    <\?.*?\?> | <%.*?%>     # processing instruction
                |
                    <[!$]?[-a-zA-Z0-9:_]+   # regular tags
                    (?>
                        \s
                        (?>[^"\'>]+|"[^"]*"|\'[^\']*\')*
                    )?
                    >
                |
                    <[-a-zA-Z0-9:_]+\s*/> # xml-style empty tag
                |
                    </[-a-zA-Z0-9:_]+\s*> # closing tag
            ').'
                )
                }xs';

        while (1) {
            #
            # Each loop iteration seach for either the next tag, the next 
            # openning code span marker, or the next escaped character. 
            # Each token is then passed to handleSpanToken.
            #
            $parts = preg_split($span_re, $str, 2, PREG_SPLIT_DELIM_CAPTURE);
            
            # Create token from text preceding tag.
            if ($parts[0] != "") {
                $output .= $parts[0];
            }
            
            # Check if we reach the end.
            if (isset($parts[1])) {
                $output .= $this->handleSpanToken($parts[1], $parts[2]);
                $str = $parts[2];
            }
            else {
                break;
            }
        }
        
        return $output;
    }
    
    
    protected function handleSpanToken($token, &$str) {
    #
    # Handle $token provided by parseSpan by determining its nature and 
    # returning the corresponding value that should replace it.
    #
        switch ($token{0}) {
            case "\\":
                return $this->hashPart("&#". ord($token{1}). ";");
            case "`":
                # Search for end marker in remaining text.
                if (preg_match('/^(.*?[^`])'.preg_quote($token).'(?!`)(.*)$/sm', 
                    $str, $matches))
                {
                    $str = $matches[2];
                    $codespan = $this->makeCodeSpan($matches[1]);
                    return $this->hashPart($codespan);
                }
                return $token; // return as text since no ending marker found.
            default:
                return $this->hashPart($token);
        }
    }


    protected function outdent($text) {
    #
    # Remove one level of line-leading tabs or spaces
    #
        return preg_replace('/^(\t|[ ]{1,'.$this->tab_width.'})/m', '', $text);
    }


    # String length function for detab. `_initDetab` will create a function to 
    # hanlde UTF-8 if the default function does not exist.
    protected $utf8_strlen = 'mb_strlen';
    
    protected function detab($text) {
    #
    # Replace tabs with the appropriate amount of space.
    #
        # For each line we separate the line in blocks delemited by
        # tab characters. Then we reconstruct every line by adding the 
        # appropriate number of space between each blocks.
        
        $text = preg_replace_callback('/^.*\t.*$/m',
            array($this, '_detab_callback'), $text);

        return $text;
    }
    protected function _detab_callback($matches) {
        $line = $matches[0];
        $strlen = $this->utf8_strlen; # strlen function for UTF-8.
        
        # Split in blocks.
        $blocks = explode("\t", $line);
        # Add each blocks to the line.
        $line = $blocks[0];
        unset($blocks[0]); # Do not add first block twice.
        foreach ($blocks as $block) {
            # Calculate amount of space, insert spaces, insert block.
            $amount = $this->tab_width - 
                call_user_func($strlen, $line, 'UTF-8') % $this->tab_width;
            $line .= str_repeat(" ", $amount) . $block;
        }
        return $line;
    }
    protected function _initDetab() {
    #
    # Check for the availability of the function in the `utf8_strlen` property
    # (initially `mb_strlen`). If the function is not available, create a 
    # function that will loosely count the number of UTF-8 characters with a
    # regular expression.
    #
        if (function_exists($this->utf8_strlen)) return;
        $this->utf8_strlen = array($this, '_utf8_strlen');
    }

    protected function _utf8_strlen($text) {
        return preg_match_all(
            "/[\\x00-\\xBF]|[\\xC0-\\xFF][\\x80-\\xBF]*/", 
            $text, $m);
    }


    protected function unhash($text) {
    #
    # Swap back in all the tags hashed by _HashHTMLBlocks.
    #
        return preg_replace_callback('/(.)\x1A[0-9]+\1/', 
            array($this, '_unhash_callback'), $text);
    }
    protected function _unhash_callback($matches) {
        return $this->html_hashes[trim($matches[0])];
    }
}

#
# Temporary Markdown Extra Parser Implementation Class
#
# NOTE: DON'T USE THIS CLASS
# Currently the implementation of of Extra resides here in this temporary class.
# This makes it easier to propagate the changes between the three different
# packaging styles of PHP Markdown. When this issue is resolved, this
# MarkdownExtra_TmpImpl class here will disappear and \Michelf\MarkdownExtra
# will contain the code. So please use \Michelf\MarkdownExtra and ignore this
# one.
#

class MarkdownExtra extends _Markdown {

    ### Configuration Variables ###

    # Prefix for footnote ids.
    public $fn_id_prefix = "";
    
    # Optional title attribute for footnote links and backlinks.
    public $fn_link_title = "";
    public $fn_backlink_title = "";
    
    # Optional class attribute for footnote links and backlinks.
    public $fn_link_class = "footnote-ref";
    public $fn_backlink_class = "footnote-backref";

    # Class name for table cell alignment (%% replaced left/center/right)
    # For instance: 'go-%%' becomes 'go-left' or 'go-right' or 'go-center'
    # If empty, the align attribute is used instead of a class name.
    public $table_align_class_tmpl = '';

    # Optional class prefix for fenced code block.
    public $code_class_prefix = "";
    # Class attribute for code blocks goes on the `code` tag;
    # setting this to true will put attributes on the `pre` tag instead.
    public $code_attr_on_pre = false;
    
    # Predefined abbreviations.
    public $predef_abbr = array();


    ### Parser Implementation ###

    public function __construct() {
    #
    # Constructor function. Initialize the parser object.
    #
        # Add extra escapable characters before parent constructor 
        # initialize the table.
        $this->escape_chars .= ':|';
        
        # Insert extra document, block, and span transformations. 
        # Parent constructor will do the sorting.
        $this->document_gamut += array(
            "doFencedCodeBlocks" => 5,
            "stripFootnotes"     => 15,
            "stripAbbreviations" => 25,
            "appendFootnotes"    => 50,
            );
        $this->block_gamut += array(
            "doFencedCodeBlocks" => 5,
            "doTables"           => 15,
            "doDefLists"         => 45,
            );
        $this->span_gamut += array(
            "doFootnotes"        => 5,
            "doAbbreviations"    => 70,
            );
        
        parent::__construct();
    }
    
    
    # Extra variables used during extra transformations.
    protected $footnotes = array();
    protected $footnotes_ordered = array();
    protected $footnotes_ref_count = array();
    protected $footnotes_numbers = array();
    protected $abbr_desciptions = array();
    protected $abbr_word_re = '';
    
    # Give the current footnote number.
    protected $footnote_counter = 1;
    
    
    protected function setup() {
    #
    # Setting up Extra-specific variables.
    #
        parent::setup();
        
        $this->footnotes = array();
        $this->footnotes_ordered = array();
        $this->footnotes_ref_count = array();
        $this->footnotes_numbers = array();
        $this->abbr_desciptions = array();
        $this->abbr_word_re = '';
        $this->footnote_counter = 1;
        
        foreach ($this->predef_abbr as $abbr_word => $abbr_desc) {
            if ($this->abbr_word_re)
                $this->abbr_word_re .= '|';
            $this->abbr_word_re .= preg_quote($abbr_word);
            $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);
        }
    }
    
    protected function teardown() {
    #
    # Clearing Extra-specific variables.
    #
        $this->footnotes = array();
        $this->footnotes_ordered = array();
        $this->footnotes_ref_count = array();
        $this->footnotes_numbers = array();
        $this->abbr_desciptions = array();
        $this->abbr_word_re = '';
        
        parent::teardown();
    }
    
    
    ### Extra Attribute Parser ###

    # Expression to use to catch attributes (includes the braces)
    protected $id_class_attr_catch_re = '\{((?:[ ]*[#.][-_:a-zA-Z0-9]+){1,})[ ]*\}';
    # Expression to use when parsing in a context when no capture is desired
    protected $id_class_attr_nocatch_re = '\{(?:[ ]*[#.][-_:a-zA-Z0-9]+){1,}[ ]*\}';

    protected function doExtraAttributes($tag_name, $attr) {
    #
    # Parse attributes caught by the $this->id_class_attr_catch_re expression
    # and return the HTML-formatted list of attributes.
    #
    # Currently supported attributes are .class and #id.
    #
        if (empty($attr)) return "";
        
        # Split on components
        preg_match_all('/[#.][-_:a-zA-Z0-9]+/', $attr, $matches);
        $elements = $matches[0];

        # handle classes and ids (only first id taken into account)
        $classes = array();
        $id = false;
        foreach ($elements as $element) {
            if ($element{0} == '.') {
                $classes[] = substr($element, 1);
            } else if ($element{0} == '#') {
                if ($id === false) $id = substr($element, 1);
            }
        }

        # compose attributes as string
        $attr_str = "";
        if (!empty($id)) {
            $attr_str .= ' id="'.$id.'"';
        }
        if (!empty($classes)) {
            $attr_str .= ' class="'.implode(" ", $classes).'"';
        }
        return $attr_str;
    }


    protected function stripLinkDefinitions($text) {
    #
    # Strips link definitions from text, stores the URLs and titles in
    # hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: ^[id]: url "optional title"
        $text = preg_replace_callback('{
                            ^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?: # id = $1
                              [ ]*
                              \n?               # maybe *one* newline
                              [ ]*
                            (?:
                              <(.+?)>           # url = $2
                            |
                              (\S+?)            # url = $3
                            )
                              [ ]*
                              \n?               # maybe one newline
                              [ ]*
                            (?:
                                (?<=\s)         # lookbehind for whitespace
                                ["(]
                                (.*?)           # title = $4
                                [")]
                                [ ]*
                            )?  # title is optional
                    (?:[ ]* '.$this->id_class_attr_catch_re.' )?  # $5 = extra id & class attr
                            (?:\n+|\Z)
            }xm',
            array($this, '_stripLinkDefinitions_callback'),
            $text);
        return $text;
    }
    protected function _stripLinkDefinitions_callback($matches) {
        $link_id = strtolower($matches[1]);
        $url = $matches[2] == '' ? $matches[3] : $matches[2];
        $this->urls[$link_id] = $url;
        $this->titles[$link_id] =& $matches[4];
        $this->ref_attr[$link_id] = $this->doExtraAttributes("", $dummy =& $matches[5]);
        return ''; # String that will replace the block
    }


    ### HTML Block Parser ###
    
    # Tags that are always treated as block tags:
    protected $block_tags_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|form|fieldset|iframe|hr|legend|article|section|nav|aside|hgroup|header|footer|figcaption';
                           
    # Tags treated as block tags only if the opening tag is alone on its line:
    protected $context_block_tags_re = 'script|noscript|ins|del|iframe|object|source|track|param|math|svg|canvas|audio|video';
    
    # Tags where markdown="1" default to span mode:
    protected $contain_span_tags_re = 'p|h[1-6]|li|dd|dt|td|th|legend|address';
    
    # Tags which must not have their contents modified, no matter where 
    # they appear:
    protected $clean_tags_re = 'script|math|svg';
    
    # Tags that do not need to be closed.
    protected $auto_close_tags_re = 'hr|img|param|source|track';
    

    protected function hashHTMLBlocks($text) {
    #
    # Hashify HTML Blocks and "clean tags".
    #
    # We only want to do this for block-level HTML tags, such as headers,
    # lists, and tables. That's because we still want to wrap <p>s around
    # "paragraphs" that are wrapped in non-block-level tags, such as anchors,
    # phrase emphasis, and spans. The list of tags we're looking for is
    # hard-coded.
    #
    # This works by calling _HashHTMLBlocks_InMarkdown, which then calls
    # _HashHTMLBlocks_InHTML when it encounter block tags. When the markdown="1" 
    # attribute is found within a tag, _HashHTMLBlocks_InHTML calls back
    #  _HashHTMLBlocks_InMarkdown to handle the Markdown syntax within the tag.
    # These two functions are calling each other. It's recursive!
    #
        if ($this->no_markup)  return $text;

        #
        # Call the HTML-in-Markdown hasher.
        #
        list($text, ) = $this->_hashHTMLBlocks_inMarkdown($text);
        
        return $text;
    }
    protected function _hashHTMLBlocks_inMarkdown($text, $indent = 0,
                                        $enclosing_tag_re = '', $span = false)
    {
    #
    # Parse markdown text, calling _HashHTMLBlocks_InHTML for block tags.
    #
    # *   $indent is the number of space to be ignored when checking for code 
    #     blocks. This is important because if we don't take the indent into 
    #     account, something like this (which looks right) won't work as expected:
    #
    #     <div>
    #         <div markdown="1">
    #         Hello World.  <-- Is this a Markdown code block or text?
    #         </div>  <-- Is this a Markdown code block or a real tag?
    #     <div>
    #
    #     If you don't like this, just don't indent the tag on which
    #     you apply the markdown="1" attribute.
    #
    # *   If $enclosing_tag_re is not empty, stops at the first unmatched closing 
    #     tag with that name. Nested tags supported.
    #
    # *   If $span is true, text inside must treated as span. So any double 
    #     newline will be replaced by a single newline so that it does not create 
    #     paragraphs.
    #
    # Returns an array of that form: ( processed text , remaining text )
    #
        if ($text === '') return array('', '');

        # Regex to check for the presense of newlines around a block tag.
        $newline_before_re = '/(?:^\n?|\n\n)*$/';
        $newline_after_re = 
            '{
                ^                       # Start of text following the tag.
                (?>[ ]*<!--.*?-->)?     # Optional comment.
                [ ]*\n                  # Must be followed by newline.
            }xs';
        
        # Regex to match any tag.
        $block_tag_re =
            '{
                (                   # $2: Capture whole tag.
                    </?                 # Any opening or closing tag.
                        (?>             # Tag name.
                            '.$this->block_tags_re.'            |
                            '.$this->context_block_tags_re.'    |
                            '.$this->clean_tags_re.'            |
                            (?!\s)'.$enclosing_tag_re.'
                        )
                        (?:
                            (?=[\s"\'/a-zA-Z0-9])   # Allowed characters after tag name.
                            (?>
                                ".*?"       |   # Double quotes (can contain `>`)
                                \'.*?\'     |   # Single quotes (can contain `>`)
                                .+?             # Anything but quotes and `>`.
                            )*?
                        )?
                    >                   # End of tag.
                |
                    <!--    .*?     --> # HTML Comment
                |
                    <\?.*?\?> | <%.*?%> # Processing instruction
                |
                    <!\[CDATA\[.*?\]\]> # CData Block
                |
                    # Code span marker
                    `+
                '. ( !$span ? ' # If not in span.
                |
                    # Indented code block
                    (?: ^[ ]*\n | ^ | \n[ ]*\n )
                    [ ]{'.($indent+4).'}[^\n]* \n
                    (?>
                        (?: [ ]{'.($indent+4).'}[^\n]* | [ ]* ) \n
                    )*
                |
                    # Fenced code block marker
                    (?<= ^ | \n )
                    [ ]{0,'.($indent+3).'}~{3,}
                                    [ ]*
                    (?:
                    \.?[-_:a-zA-Z0-9]+ # standalone class name
                    |
                        '.$this->id_class_attr_nocatch_re.' # extra attributes
                    )?
                    [ ]*
                    \n
                ' : '' ). ' # End (if not is span).
                )
            }xs';

        
        $depth = 0;     # Current depth inside the tag tree.
        $parsed = "";   # Parsed text that will be returned.

        #
        # Loop through every tag until we find the closing tag of the parent
        # or loop until reaching the end of text if no parent tag specified.
        #
        do {
            #
            # Split the text using the first $tag_match pattern found.
            # Text before  pattern will be first in the array, text after
            # pattern will be at the end, and between will be any catches made 
            # by the pattern.
            #
            $parts = preg_split($block_tag_re, $text, 2, 
                                PREG_SPLIT_DELIM_CAPTURE);
            
            # If in Markdown span mode, add a empty-string span-level hash 
            # after each newline to prevent triggering any block element.
            if ($span) {
                $void = $this->hashPart("", ':');
                $newline = "$void\n";
                $parts[0] = $void . str_replace("\n", $newline, $parts[0]) . $void;
            }
            
            $parsed .= $parts[0]; # Text before current tag.
            
            # If end of $text has been reached. Stop loop.
            if (count($parts) < 3) {
                $text = "";
                break;
            }
            
            $tag  = $parts[1]; # Tag to handle.
            $text = $parts[2]; # Remaining text after current tag.
            $tag_re = preg_quote($tag); # For use in a regular expression.
            
            #
            # Check for: Code span marker
            #
            if ($tag{0} == "`") {
                # Find corresponding end marker.
                $tag_re = preg_quote($tag);
                if (preg_match('{^(?>.+?|\n(?!\n))*?(?<!`)'.$tag_re.'(?!`)}',
                    $text, $matches))
                {
                    # End marker found: pass text unchanged until marker.
                    $parsed .= $tag . $matches[0];
                    $text = substr($text, strlen($matches[0]));
                }
                else {
                    # Unmatched marker: just skip it.
                    $parsed .= $tag;
                }
            }
            #
            # Check for: Fenced code block marker.
            #
            else if (preg_match('{^\n?([ ]{0,'.($indent+3).'})(~+)}', $tag, $capture)) {
                # Fenced code block marker: find matching end marker.
                $fence_indent = strlen($capture[1]); # use captured indent in re
                $fence_re = $capture[2]; # use captured fence in re
                if (preg_match('{^(?>.*\n)*?[ ]{'.($fence_indent).'}'.$fence_re.'[ ]*(?:\n|$)}', $text,
                    $matches)) 
                {
                    # End marker found: pass text unchanged until marker.
                    $parsed .= $tag . $matches[0];
                    $text = substr($text, strlen($matches[0]));
                }
                else {
                    # No end marker: just skip it.
                    $parsed .= $tag;
                }
            }
            #
            # Check for: Indented code block.
            #
            else if ($tag{0} == "\n" || $tag{0} == " ") {
                # Indented code block: pass it unchanged, will be handled 
                # later.
                $parsed .= $tag;
            }
            #
            # Check for: Opening Block level tag or
            #            Opening Context Block tag (like ins and del) 
            #               used as a block tag (tag is alone on it's line).
            #
            else if (preg_match('{^<(?:'.$this->block_tags_re.')\b}', $tag) ||
                (   preg_match('{^<(?:'.$this->context_block_tags_re.')\b}', $tag) &&
                    preg_match($newline_before_re, $parsed) &&
                    preg_match($newline_after_re, $text)    )
                )
            {
                # Need to parse tag and following text using the HTML parser.
                list($block_text, $text) = 
                    $this->_hashHTMLBlocks_inHTML($tag . $text, "hashBlock", true);
                
                # Make sure it stays outside of any paragraph by adding newlines.
                $parsed .= "\n\n$block_text\n\n";
            }
            #
            # Check for: Clean tag (like script, math)
            #            HTML Comments, processing instructions.
            #
            else if (preg_match('{^<(?:'.$this->clean_tags_re.')\b}', $tag) ||
                $tag{1} == '!' || $tag{1} == '?')
            {
                # Need to parse tag and following text using the HTML parser.
                # (don't check for markdown attribute)
                list($block_text, $text) = 
                    $this->_hashHTMLBlocks_inHTML($tag . $text, "hashClean", false);
                
                $parsed .= $block_text;
            }
            #
            # Check for: Tag with same name as enclosing tag.
            #
            else if ($enclosing_tag_re !== '' &&
                # Same name as enclosing tag.
                preg_match('{^</?(?:'.$enclosing_tag_re.')\b}', $tag))
            {
                #
                # Increase/decrease nested tag count.
                #
                if ($tag{1} == '/')                     $depth--;
                else if ($tag{strlen($tag)-2} != '/')   $depth++;

                if ($depth < 0) {
                    #
                    # Going out of parent element. Clean up and break so we
                    # return to the calling function.
                    #
                    $text = $tag . $text;
                    break;
                }
                
                $parsed .= $tag;
            }
            else {
                $parsed .= $tag;
            }
        } while ($depth >= 0);
        
        return array($parsed, $text);
    }
    protected function _hashHTMLBlocks_inHTML($text, $hash_method, $md_attr) {
    #
    # Parse HTML, calling _HashHTMLBlocks_InMarkdown for block tags.
    #
    # *   Calls $hash_method to convert any blocks.
    # *   Stops when the first opening tag closes.
    # *   $md_attr indicate if the use of the `markdown="1"` attribute is allowed.
    #     (it is not inside clean tags)
    #
    # Returns an array of that form: ( processed text , remaining text )
    #
        if ($text === '') return array('', '');
        
        # Regex to match `markdown` attribute inside of a tag.
        $markdown_attr_re = '
            {
                \s*         # Eat whitespace before the `markdown` attribute
                markdown
                \s*=\s*
                (?>
                    (["\'])     # $1: quote delimiter       
                    (.*?)       # $2: attribute value
                    \1          # matching delimiter    
                |
                    ([^\s>]*)   # $3: unquoted attribute value
                )
                ()              # $4: make $3 always defined (avoid warnings)
            }xs';
        
        # Regex to match any tag.
        $tag_re = '{
                (                   # $2: Capture whole tag.
                    </?                 # Any opening or closing tag.
                        [\w:$]+         # Tag name.
                        (?:
                            (?=[\s"\'/a-zA-Z0-9])   # Allowed characters after tag name.
                            (?>
                                ".*?"       |   # Double quotes (can contain `>`)
                                \'.*?\'     |   # Single quotes (can contain `>`)
                                .+?             # Anything but quotes and `>`.
                            )*?
                        )?
                    >                   # End of tag.
                |
                    <!--    .*?     --> # HTML Comment
                |
                    <\?.*?\?> | <%.*?%> # Processing instruction
                |
                    <!\[CDATA\[.*?\]\]> # CData Block
                )
            }xs';
        
        $original_text = $text;     # Save original text in case of faliure.
        
        $depth      = 0;    # Current depth inside the tag tree.
        $block_text = "";   # Temporary text holder for current text.
        $parsed     = "";   # Parsed text that will be returned.

        #
        # Get the name of the starting tag.
        # (This pattern makes $base_tag_name_re safe without quoting.)
        #
        if (preg_match('/^<([\w:$]*)\b/', $text, $matches))
            $base_tag_name_re = $matches[1];

        #
        # Loop through every tag until we find the corresponding closing tag.
        #
        do {
            #
            # Split the text using the first $tag_match pattern found.
            # Text before  pattern will be first in the array, text after
            # pattern will be at the end, and between will be any catches made 
            # by the pattern.
            #
            $parts = preg_split($tag_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
            
            if (count($parts) < 3) {
                #
                # End of $text reached with unbalenced tag(s).
                # In that case, we return original text unchanged and pass the
                # first character as filtered to prevent an infinite loop in the 
                # parent function.
                #
                return array($original_text{0}, substr($original_text, 1));
            }
            
            $block_text .= $parts[0]; # Text before current tag.
            $tag         = $parts[1]; # Tag to handle.
            $text        = $parts[2]; # Remaining text after current tag.
            
            #
            # Check for: Auto-close tag (like <hr/>)
            #            Comments and Processing Instructions.
            #
            if (preg_match('{^</?(?:'.$this->auto_close_tags_re.')\b}', $tag) ||
                $tag{1} == '!' || $tag{1} == '?')
            {
                # Just add the tag to the block as if it was text.
                $block_text .= $tag;
            }
            else {
                #
                # Increase/decrease nested tag count. Only do so if
                # the tag's name match base tag's.
                #
                if (preg_match('{^</?'.$base_tag_name_re.'\b}', $tag)) {
                    if ($tag{1} == '/')                     $depth--;
                    else if ($tag{strlen($tag)-2} != '/')   $depth++;
                }
                
                #
                # Check for `markdown="1"` attribute and handle it.
                #
                if ($md_attr && 
                    preg_match($markdown_attr_re, $tag, $attr_m) &&
                    preg_match('/^1|block|span$/', $attr_m[2] . $attr_m[3]))
                {
                    # Remove `markdown` attribute from opening tag.
                    $tag = preg_replace($markdown_attr_re, '', $tag);
                    
                    # Check if text inside this tag must be parsed in span mode.
                    $this->mode = $attr_m[2] . $attr_m[3];
                    $span_mode = $this->mode == 'span' || $this->mode != 'block' &&
                        preg_match('{^<(?:'.$this->contain_span_tags_re.')\b}', $tag);
                    
                    # Calculate indent before tag.
                    if (preg_match('/(?:^|\n)( *?)(?! ).*?$/', $block_text, $matches)) {
                        $strlen = $this->utf8_strlen;
                        $indent = call_user_func($strlen, $matches[1], 'UTF-8');
                    } else {
                        $indent = 0;
                    }
                    
                    # End preceding block with this tag.
                    $block_text .= $tag;
                    $parsed .= $this->$hash_method($block_text);
                    
                    # Get enclosing tag name for the ParseMarkdown function.
                    # (This pattern makes $tag_name_re safe without quoting.)
                    preg_match('/^<([\w:$]*)\b/', $tag, $matches);
                    $tag_name_re = $matches[1];
                    
                    # Parse the content using the HTML-in-Markdown parser.
                    list ($block_text, $text)
                        = $this->_hashHTMLBlocks_inMarkdown($text, $indent, 
                            $tag_name_re, $span_mode);
                    
                    # Outdent markdown text.
                    if ($indent > 0) {
                        $block_text = preg_replace("/^[ ]{1,$indent}/m", "", 
                                                    $block_text);
                    }
                    
                    # Append tag content to parsed text.
                    if (!$span_mode)    $parsed .= "\n\n$block_text\n\n";
                    else                $parsed .= "$block_text";
                    
                    # Start over with a new block.
                    $block_text = "";
                }
                else $block_text .= $tag;
            }
            
        } while ($depth > 0);
        
        #
        # Hash last block text that wasn't processed inside the loop.
        #
        $parsed .= $this->$hash_method($block_text);
        
        return array($parsed, $text);
    }


    protected function hashClean($text) {
    #
    # Called whenever a tag must be hashed when a function inserts a "clean" tag
    # in $text, it passes through this function and is automaticaly escaped, 
    # blocking invalid nested overlap.
    #
        return $this->hashPart($text, 'C');
    }


    protected function doAnchors($text) {
    #
    # Turn Markdown link shortcuts into XHTML <a> tags.
    #
        if ($this->in_anchor) return $text;
        $this->in_anchor = true;
        
        #
        # First, handle reference-style links: [link text] [id]
        #
        $text = preg_replace_callback('{
            (                   # wrap whole match in $1
              \[
                ('.$this->nested_brackets_re.') # link text = $2
              \]

              [ ]?              # one optional space
              (?:\n[ ]*)?       # one optional newline followed by spaces

              \[
                (.*?)       # id = $3
              \]
            )
            }xs',
            array($this, '_doAnchors_reference_callback'), $text);

        #
        # Next, inline-style links: [link text](url "optional title")
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              \[
                ('.$this->nested_brackets_re.') # link text = $2
              \]
              \(            # literal paren
                [ \n]*
                (?:
                    <(.+?)> # href = $3
                |
                    ('.$this->nested_url_parenthesis_re.')  # href = $4
                )
                [ \n]*
                (           # $5
                  ([\'"])   # quote char = $6
                  (.*?)     # Title = $7
                  \6        # matching quote
                  [ \n]*    # ignore any spaces/tabs between closing quote and )
                )?          # title is optional
              \)
              (?:[ ]? '.$this->id_class_attr_catch_re.' )?   # $8 = id/class attributes
            )
            }xs',
            array($this, '_doAnchors_inline_callback'), $text);

        #
        # Last, handle reference-style shortcuts: [link text]
        # These must come last in case you've also got [link text][1]
        # or [link text](/foo)
        #
        $text = preg_replace_callback('{
            (                   # wrap whole match in $1
              \[
                ([^\[\]]+)      # link text = $2; can\'t contain [ or ]
              \]
            )
            }xs',
            array($this, '_doAnchors_reference_callback'), $text);

        $this->in_anchor = false;
        return $text;
    }
    protected function _doAnchors_reference_callback($matches) {
        $whole_match =  $matches[1];
        $link_text   =  $matches[2];
        $link_id     =& $matches[3];

        if ($link_id == "") {
            # for shortcut links like [this][] or [this].
            $link_id = $link_text;
        }
        
        # lower-case and turn embedded newlines into spaces
        $link_id = strtolower($link_id);
        $link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

        if (isset($this->urls[$link_id])) {
            $url = $this->urls[$link_id];
            $url = $this->encodeAttribute($url);
            
            $result = "<a href=\"$url\"";
            if ( isset( $this->titles[$link_id] ) ) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
            if (isset($this->ref_attr[$link_id]))
                $result .= $this->ref_attr[$link_id];
        
            $link_text = $this->runSpanGamut($link_text);
            $result .= ">$link_text</a>";
            $result = $this->hashPart($result);
        }
        else {
            $result = $whole_match;
        }
        return $result;
    }
    protected function _doAnchors_inline_callback($matches) {
        $whole_match    =  $matches[1];
        $link_text      =  $this->runSpanGamut($matches[2]);
        $url            =  $matches[3] == '' ? $matches[4] : $matches[3];
        $title          =& $matches[7];
        $attr  = $this->doExtraAttributes("a", $dummy =& $matches[8]);


        $url = $this->encodeAttribute($url);

        $result = "<a href=\"$url\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\"";
        }
        $result .= $attr;
        
        $link_text = $this->runSpanGamut($link_text);
        $result .= ">$link_text</a>";

        return $this->hashPart($result);
    }


    protected function doImages($text) {
    #
    # Turn Markdown image shortcuts into <img> tags.
    #
        #
        # First, handle reference-style labeled images: ![alt text][id]
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              !\[
                ('.$this->nested_brackets_re.')     # alt text = $2
              \]

              [ ]?              # one optional space
              (?:\n[ ]*)?       # one optional newline followed by spaces

              \[
                (.*?)       # id = $3
              \]

            )
            }xs', 
            array($this, '_doImages_reference_callback'), $text);

        #
        # Next, handle inline images:  ![alt text](url "optional title")
        # Don't forget: encode * and _
        #
        $text = preg_replace_callback('{
            (               # wrap whole match in $1
              !\[
                ('.$this->nested_brackets_re.')     # alt text = $2
              \]
              \s?           # One optional whitespace character
              \(            # literal paren
                [ \n]*
                (?:
                    <(\S*)> # src url = $3
                |
                    ('.$this->nested_url_parenthesis_re.')  # src url = $4
                )
                [ \n]*
                (           # $5
                  ([\'"])   # quote char = $6
                  (.*?)     # title = $7
                  \6        # matching quote
                  [ \n]*
                )?          # title is optional
              \)
              (?:[ ]? '.$this->id_class_attr_catch_re.' )?   # $8 = id/class attributes
            )
            }xs',
            array($this, '_doImages_inline_callback'), $text);

        return $text;
    }
    protected function _doImages_reference_callback($matches) {
        $whole_match = $matches[1];
        $alt_text    = $matches[2];
        $link_id     = strtolower($matches[3]);

        if ($link_id == "") {
            $link_id = strtolower($alt_text); # for shortcut links like ![this][].
        }

        $alt_text = $this->encodeAttribute($alt_text);
        if (isset($this->urls[$link_id])) {
            $url = $this->encodeAttribute($this->urls[$link_id]);
            $result = "<img src=\"$url\" alt=\"$alt_text\"";
            if (isset($this->titles[$link_id])) {
                $title = $this->titles[$link_id];
                $title = $this->encodeAttribute($title);
                $result .=  " title=\"$title\"";
            }
            if (isset($this->ref_attr[$link_id]))
                $result .= $this->ref_attr[$link_id];
            $result .= $this->empty_element_suffix;
            $result = $this->hashPart($result);
        }
        else {
            # If there's no such link ID, leave intact:
            $result = $whole_match;
        }

        return $result;
    }
    protected function _doImages_inline_callback($matches) {
        $whole_match    = $matches[1];
        $alt_text       = $matches[2];
        $url            = $matches[3] == '' ? $matches[4] : $matches[3];
        $title          =& $matches[7];
        $attr  = $this->doExtraAttributes("img", $dummy =& $matches[8]);

        $alt_text = $this->encodeAttribute($alt_text);
        $url = $this->encodeAttribute($url);
        $result = "<img src=\"$url\" alt=\"$alt_text\"";
        if (isset($title)) {
            $title = $this->encodeAttribute($title);
            $result .=  " title=\"$title\""; # $title already quoted
        }
        $result .= $attr;
        $result .= $this->empty_element_suffix;

        return $this->hashPart($result);
    }


    protected function doHeaders($text) {
    #
    # Redefined to add id and class attribute support.
    #
        # Setext-style headers:
        #     Header 1  {#header1}
        #     ========
        #  
        #     Header 2  {#header2 .class1 .class2}
        #     --------
        #
        $text = preg_replace_callback(
            '{
                (^.+?)                              # $1: Header text
                (?:[ ]+ '.$this->id_class_attr_catch_re.' )?     # $3 = id/class attributes
                [ ]*\n(=+|-+)[ ]*\n+                # $3: Header footer
            }mx',
            array($this, '_doHeaders_callback_setext'), $text);

        # atx-style headers:
        #   # Header 1        {#header1}
        #   ## Header 2       {#header2}
        #   ## Header 2 with closing hashes ##  {#header3.class1.class2}
        #   ...
        #   ###### Header 6   {.class2}
        #
        $text = preg_replace_callback('{
                ^(\#{1,6})  # $1 = string of #\'s
                [ ]*
                (.+?)       # $2 = Header text
                [ ]*
                \#*         # optional closing #\'s (not counted)
                (?:[ ]+ '.$this->id_class_attr_catch_re.' )?     # $3 = id/class attributes
                [ ]*
                \n+
            }xm',
            array($this, '_doHeaders_callback_atx'), $text);

        return $text;
    }
    protected function _doHeaders_callback_setext($matches) {
        if ($matches[3] == '-' && preg_match('{^- }', $matches[1]))
            return $matches[0];
        $level = $matches[3]{0} == '=' ? 1 : 2;
        $attr  = $this->doExtraAttributes("h$level", $dummy =& $matches[2]);
        $block = "<h$level$attr>".$this->runSpanGamut($matches[1])."</h$level>";
        return "\n" . $this->hashBlock($block) . "\n\n";
    }
    protected function _doHeaders_callback_atx($matches) {
        $level = strlen($matches[1]);
        $attr  = $this->doExtraAttributes("h$level", $dummy =& $matches[3]);
        $block = "<h$level$attr>".$this->runSpanGamut($matches[2])."</h$level>";
        return "\n" . $this->hashBlock($block) . "\n\n";
    }


    protected function doTables($text) {
    #
    # Form HTML tables.
    #
        $less_than_tab = $this->tab_width - 1;
        #
        # Find tables with leading pipe.
        #
        #   | Header 1 | Header 2
        #   | -------- | --------
        #   | Cell 1   | Cell 2
        #   | Cell 3   | Cell 4
        #
        $text = preg_replace_callback('
            {
                ^                           # Start of a line
                [ ]{0,'.$less_than_tab.'}   # Allowed whitespace.
                [|]                         # Optional leading pipe (present)
                (.+) \n                     # $1: Header row (at least one pipe)
                
                [ ]{0,'.$less_than_tab.'}   # Allowed whitespace.
                [|] ([ ]*[-:]+[-| :]*) \n   # $2: Header underline
                
                (                           # $3: Cells
                    (?>
                        [ ]*                # Allowed whitespace.
                        [|] .* \n           # Row content.
                    )*
                )
                (?=\n|\Z)                   # Stop at final double newline.
            }xm',
            array($this, '_doTable_leadingPipe_callback'), $text);
        
        #
        # Find tables without leading pipe.
        #
        #   Header 1 | Header 2
        #   -------- | --------
        #   Cell 1   | Cell 2
        #   Cell 3   | Cell 4
        #
        $text = preg_replace_callback('
            {
                ^                           # Start of a line
                [ ]{0,'.$less_than_tab.'}   # Allowed whitespace.
                (\S.*[|].*) \n              # $1: Header row (at least one pipe)
                
                [ ]{0,'.$less_than_tab.'}   # Allowed whitespace.
                ([-:]+[ ]*[|][-| :]*) \n    # $2: Header underline
                
                (                           # $3: Cells
                    (?>
                        .* [|] .* \n        # Row content
                    )*
                )
                (?=\n|\Z)                   # Stop at final double newline.
            }xm',
            array($this, '_DoTable_callback'), $text);

        return $text;
    }
    protected function _doTable_leadingPipe_callback($matches) {
        $head       = $matches[1];
        $underline  = $matches[2];
        $content    = $matches[3];
        
        # Remove leading pipe for each row.
        $content    = preg_replace('/^ *[|]/m', '', $content);
        
        return $this->_doTable_callback(array($matches[0], $head, $underline, $content));
    }
    protected function _doTable_makeAlignAttr($alignname)
    {
        if (empty($this->table_align_class_tmpl))
            return " align=\"$alignname\"";

        $classname = str_replace('%%', $alignname, $this->table_align_class_tmpl);
        return " class=\"$classname\"";
    }
    protected function _doTable_callback($matches) {
        $head       = $matches[1];
        $underline  = $matches[2];
        $content    = $matches[3];

        # Remove any tailing pipes for each line.
        $head       = preg_replace('/[|] *$/m', '', $head);
        $underline  = preg_replace('/[|] *$/m', '', $underline);
        $content    = preg_replace('/[|] *$/m', '', $content);
        
        # Reading alignement from header underline.
        $separators = preg_split('/ *[|] */', $underline);
        foreach ($separators as $n => $s) {
            if (preg_match('/^ *-+: *$/', $s))
                $attr[$n] = $this->_doTable_makeAlignAttr('right');
            else if (preg_match('/^ *:-+: *$/', $s))
                $attr[$n] = $this->_doTable_makeAlignAttr('center');
            else if (preg_match('/^ *:-+ *$/', $s))
                $attr[$n] = $this->_doTable_makeAlignAttr('left');
            else
                $attr[$n] = '';
        }
        
        # Parsing span elements, including code spans, character escapes, 
        # and inline HTML tags, so that pipes inside those gets ignored.
        $head       = $this->parseSpan($head);
        $headers    = preg_split('/ *[|] */', $head);
        $col_count  = count($headers);
        $attr       = array_pad($attr, $col_count, '');
        
        # Write column headers.
        $text = "<table>\n";
        $text .= "<thead>\n";
        $text .= "<tr>\n";
        foreach ($headers as $n => $header)
            $text .= "  <th$attr[$n]>".$this->runSpanGamut(trim($header))."</th>\n";
        $text .= "</tr>\n";
        $text .= "</thead>\n";
        
        # Split content by row.
        $rows = explode("\n", trim($content, "\n"));
        
        $text .= "<tbody>\n";
        foreach ($rows as $row) {
            # Parsing span elements, including code spans, character escapes, 
            # and inline HTML tags, so that pipes inside those gets ignored.
            $row = $this->parseSpan($row);
            
            # Split row by cell.
            $row_cells = preg_split('/ *[|] */', $row, $col_count);
            $row_cells = array_pad($row_cells, $col_count, '');
            
            $text .= "<tr>\n";
            foreach ($row_cells as $n => $cell)
                $text .= "  <td$attr[$n]>".$this->runSpanGamut(trim($cell))."</td>\n";
            $text .= "</tr>\n";
        }
        $text .= "</tbody>\n";
        $text .= "</table>";
        
        return $this->hashBlock($text) . "\n";
    }

    
    protected function doDefLists($text) {
    #
    # Form HTML definition lists.
    #
        $less_than_tab = $this->tab_width - 1;

        # Re-usable pattern to match any entire dl list:
        $whole_list_re = '(?>
            (                               # $1 = whole list
              (                             # $2
                [ ]{0,'.$less_than_tab.'}
                ((?>.*\S.*\n)+)             # $3 = defined term
                \n?
                [ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
              )
              (?s:.+?)
              (                             # $4
                  \z
                |
                  \n{2,}
                  (?=\S)
                  (?!                       # Negative lookahead for another term
                    [ ]{0,'.$less_than_tab.'}
                    (?: \S.*\n )+?          # defined term
                    \n?
                    [ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
                  )
                  (?!                       # Negative lookahead for another definition
                    [ ]{0,'.$less_than_tab.'}:[ ]+ # colon starting definition
                  )
              )
            )
        )'; // mx

        $text = preg_replace_callback('{
                (?>\A\n?|(?<=\n\n))
                '.$whole_list_re.'
            }mx',
            array($this, '_doDefLists_callback'), $text);

        return $text;
    }
    protected function _doDefLists_callback($matches) {
        # Re-usable patterns to match list item bullets and number markers:
        $list = $matches[1];
        
        # Turn double returns into triple returns, so that we can make a
        # paragraph for the last item in a list, if necessary:
        $result = trim($this->processDefListItems($list));
        $result = "<dl>\n" . $result . "\n</dl>";
        return $this->hashBlock($result) . "\n\n";
    }


    protected function processDefListItems($list_str) {
    #
    #   Process the contents of a single definition list, splitting it
    #   into individual term and definition list items.
    #
        $less_than_tab = $this->tab_width - 1;
        
        # trim trailing blank lines:
        $list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

        # Process definition terms.
        $list_str = preg_replace_callback('{
            (?>\A\n?|\n\n+)                 # leading line
            (                               # definition terms = $1
                [ ]{0,'.$less_than_tab.'}   # leading whitespace
                (?!\:[ ]|[ ])               # negative lookahead for a definition
                                            #   mark (colon) or more whitespace.
                (?> \S.* \n)+?              # actual term (not whitespace). 
            )           
            (?=\n?[ ]{0,3}:[ ])             # lookahead for following line feed 
                                            #   with a definition mark.
            }xm',
            array($this, '_processDefListItems_callback_dt'), $list_str);

        # Process actual definitions.
        $list_str = preg_replace_callback('{
            \n(\n+)?                        # leading line = $1
            (                               # marker space = $2
                [ ]{0,'.$less_than_tab.'}   # whitespace before colon
                \:[ ]+                      # definition mark (colon)
            )
            ((?s:.+?))                      # definition text = $3
            (?= \n+                         # stop at next definition mark,
                (?:                         # next term or end of text
                    [ ]{0,'.$less_than_tab.'} \:[ ] |
                    <dt> | \z
                )                       
            )                   
            }xm',
            array($this, '_processDefListItems_callback_dd'), $list_str);

        return $list_str;
    }
    protected function _processDefListItems_callback_dt($matches) {
        $terms = explode("\n", trim($matches[1]));
        $text = '';
        foreach ($terms as $term) {
            $term = $this->runSpanGamut(trim($term));
            $text .= "\n<dt>" . $term . "</dt>";
        }
        return $text . "\n";
    }
    protected function _processDefListItems_callback_dd($matches) {
        $leading_line   = $matches[1];
        $marker_space   = $matches[2];
        $def            = $matches[3];

        if ($leading_line || preg_match('/\n{2,}/', $def)) {
            # Replace marker with the appropriate whitespace indentation
            $def = str_repeat(' ', strlen($marker_space)) . $def;
            $def = $this->runBlockGamut($this->outdent($def . "\n\n"));
            $def = "\n". $def ."\n";
        }
        else {
            $def = rtrim($def);
            $def = $this->runSpanGamut($this->outdent($def));
        }

        return "\n<dd>" . $def . "</dd>\n";
    }


    protected function doFencedCodeBlocks($text) {
    #
    # Adding the fenced code block syntax to regular Markdown:
    #
    # ~~~
    # Code block
    # ~~~
    #
        $less_than_tab = $this->tab_width;
        
        $text = preg_replace_callback('{
                (?:\n|\A)
                # 1: Opening marker
                (
                    ~{3,} # Marker: three tilde or more.
                )
                [ ]*
                (?:
                    \.?([-_:a-zA-Z0-9]+) # 2: standalone class name
                |
                    '.$this->id_class_attr_catch_re.' # 3: Extra attributes
                )?
                [ ]* \n # Whitespace and newline following marker.
                
                # 4: Content
                (
                    (?>
                        (?!\1 [ ]* \n)  # Not a closing marker.
                        .*\n+
                    )+
                )
                
                # Closing marker.
                \1 [ ]* \n
            }xm',
            array($this, '_doFencedCodeBlocks_callback'), $text);

        return $text;
    }
    protected function _doFencedCodeBlocks_callback($matches) {
        $classname =& $matches[2];
        $attrs     =& $matches[3];
        $codeblock = $matches[4];
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);
        $codeblock = preg_replace_callback('/^\n+/',
            array($this, '_doFencedCodeBlocks_newlines'), $codeblock);

        if ($classname != "") {
            if ($classname{0} == '.')
                $classname = substr($classname, 1);
            $attr_str = ' class="'.$this->code_class_prefix.$classname.'"';
        } else {
            $attr_str = $this->doExtraAttributes($this->code_attr_on_pre ? "pre" : "code", $attrs);
        }
        $pre_attr_str  = $this->code_attr_on_pre ? $attr_str : '';
        $code_attr_str = $this->code_attr_on_pre ? '' : $attr_str;
        $codeblock  = "<pre$pre_attr_str><code$code_attr_str>$codeblock</code></pre>";
        
        return "\n\n".$this->hashBlock($codeblock)."\n\n";
    }
    protected function _doFencedCodeBlocks_newlines($matches) {
        return str_repeat("<br$this->empty_element_suffix", 
            strlen($matches[0]));
    }


    #
    # Redefining emphasis markers so that emphasis by underscore does not
    # work in the middle of a word.
    #
    protected $em_relist = array(
        ''  => '(?:(?<!\*)\*(?!\*)|(?<![a-zA-Z0-9_])_(?!_))(?=\S|$)(?![\.,:;]\s)',
        '*' => '(?<=\S|^)(?<!\*)\*(?!\*)',
        '_' => '(?<=\S|^)(?<!_)_(?![a-zA-Z0-9_])',
        );
    protected $strong_relist = array(
        ''   => '(?:(?<!\*)\*\*(?!\*)|(?<![a-zA-Z0-9_])__(?!_))(?=\S|$)(?![\.,:;]\s)',
        '**' => '(?<=\S|^)(?<!\*)\*\*(?!\*)',
        '__' => '(?<=\S|^)(?<!_)__(?![a-zA-Z0-9_])',
        );
    protected $em_strong_relist = array(
        ''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<![a-zA-Z0-9_])___(?!_))(?=\S|$)(?![\.,:;]\s)',
        '***' => '(?<=\S|^)(?<!\*)\*\*\*(?!\*)',
        '___' => '(?<=\S|^)(?<!_)___(?![a-zA-Z0-9_])',
        );


    protected function formParagraphs($text) {
    #
    #   Params:
    #       $text - string to process with html <p> tags
    #
        # Strip leading and trailing lines:
        $text = preg_replace('/\A\n+|\n+\z/', '', $text);
        
        $grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

        #
        # Wrap <p> tags and unhashify HTML blocks
        #
        foreach ($grafs as $key => $value) {
            $value = trim($this->runSpanGamut($value));
            
            # Check if this should be enclosed in a paragraph.
            # Clean tag hashes & block tag hashes are left alone.
            $is_p = !preg_match('/^B\x1A[0-9]+B|^C\x1A[0-9]+C$/', $value);
            
            if ($is_p) {
                $value = "<p>$value</p>";
            }
            $grafs[$key] = $value;
        }
        
        # Join grafs in one text, then unhash HTML tags. 
        $text = implode("\n\n", $grafs);
        
        # Finish by removing any tag hashes still present in $text.
        $text = $this->unhash($text);
        
        return $text;
    }
    
    
    ### Footnotes
    
    protected function stripFootnotes($text) {
    #
    # Strips link definitions from text, stores the URLs and titles in
    # hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: [^id]: url "optional title"
        $text = preg_replace_callback('{
            ^[ ]{0,'.$less_than_tab.'}\[\^(.+?)\][ ]?:  # note_id = $1
              [ ]*
              \n?                   # maybe *one* newline
            (                       # text = $2 (no blank lines allowed)
                (?:                 
                    .+              # actual text
                |
                    \n              # newlines but 
                    (?!\[\^.+?\]:\s)# negative lookahead for footnote marker.
                    (?!\n+[ ]{0,3}\S)# ensure line is not blank and followed 
                                    # by non-indented content
                )*
            )       
            }xm',
            array($this, '_stripFootnotes_callback'),
            $text);
        return $text;
    }
    protected function _stripFootnotes_callback($matches) {
        $note_id = $this->fn_id_prefix . $matches[1];
        $this->footnotes[$note_id] = $this->outdent($matches[2]);
        return ''; # String that will replace the block
    }


    protected function doFootnotes($text) {
    #
    # Replace footnote references in $text [^id] with a special text-token 
    # which will be replaced by the actual footnote marker in appendFootnotes.
    #
        if (!$this->in_anchor) {
            $text = preg_replace('{\[\^(.+?)\]}', "F\x1Afn:\\1\x1A:", $text);
        }
        return $text;
    }

    
    protected function appendFootnotes($text) {
    #
    # Append footnote list to text.
    #
        $text = preg_replace_callback('{F\x1Afn:(.*?)\x1A:}', 
            array($this, '_appendFootnotes_callback'), $text);
    
        if (!empty($this->footnotes_ordered)) {
            $text .= "\n\n";
            $text .= "<div class=\"footnotes\">\n";
            $text .= "<hr". $this->empty_element_suffix ."\n";
            $text .= "<ol>\n\n";
            
            $attr = " rev=\"footnote\"";
            if ($this->fn_backlink_class != "") {
                $class = $this->fn_backlink_class;
                $class = $this->encodeAttribute($class);
                $attr .= " class=\"$class\"";
            }
            if ($this->fn_backlink_title != "") {
                $title = $this->fn_backlink_title;
                $title = $this->encodeAttribute($title);
                $attr .= " title=\"$title\"";
            }
            $num = 0;
            
            while (!empty($this->footnotes_ordered)) {
                $footnote = reset($this->footnotes_ordered);
                $note_id = key($this->footnotes_ordered);
                unset($this->footnotes_ordered[$note_id]);
                $ref_count = $this->footnotes_ref_count[$note_id];
                unset($this->footnotes_ref_count[$note_id]);
                unset($this->footnotes[$note_id]);
                
                $footnote .= "\n"; # Need to append newline before parsing.
                $footnote = $this->runBlockGamut("$footnote\n");                
                $footnote = preg_replace_callback('{F\x1Afn:(.*?)\x1A:}', 
                    array($this, '_appendFootnotes_callback'), $footnote);
                
                $attr = str_replace("%%", ++$num, $attr);
                $note_id = $this->encodeAttribute($note_id);

                # Prepare backlink, multiple backlinks if multiple references
                $backlink = "<a href=\"#fnref:$note_id\"$attr>&#8617;</a>";
                for ($ref_num = 2; $ref_num <= $ref_count; ++$ref_num) {
                    $backlink .= " <a href=\"#fnref$ref_num:$note_id\"$attr>&#8617;</a>";
                }
                # Add backlink to last paragraph; create new paragraph if needed.
                if (preg_match('{</p>$}', $footnote)) {
                    $footnote = substr($footnote, 0, -4) . "&#160;$backlink</p>";
                } else {
                    $footnote .= "\n\n<p>$backlink</p>";
                }
                
                $text .= "<li id=\"fn:$note_id\">\n";
                $text .= $footnote . "\n";
                $text .= "</li>\n\n";
            }
            
            $text .= "</ol>\n";
            $text .= "</div>";
        }
        return $text;
    }
    protected function _appendFootnotes_callback($matches) {
        $node_id = $this->fn_id_prefix . $matches[1];
        
        # Create footnote marker only if it has a corresponding footnote *and*
        # the footnote hasn't been used by another marker.
        if (isset($this->footnotes[$node_id])) {
            $num =& $this->footnotes_numbers[$node_id];
            if (!isset($num)) {
                # Transfer footnote content to the ordered list and give it its
                # number
                $this->footnotes_ordered[$node_id] = $this->footnotes[$node_id];
                $this->footnotes_ref_count[$node_id] = 1;
                $num = $this->footnote_counter++;
                $ref_count_mark = '';
            } else {
                $ref_count_mark = $this->footnotes_ref_count[$node_id] += 1;
            }

            $attr = "";
            if ($this->fn_link_class != "") {
                $class = $this->fn_link_class;
                $class = $this->encodeAttribute($class);
                $attr .= " class=\"$class\"";
            }
            if ($this->fn_link_title != "") {
                $title = $this->fn_link_title;
                $title = $this->encodeAttribute($title);
                $attr .= " title=\"$title\"";
            }
            
            $attr = str_replace("%%", $num, $attr);
            $node_id = $this->encodeAttribute($node_id);
            
            return
                "<sup id=\"fnref$ref_count_mark:$node_id\">".
                "<a href=\"#fn:$node_id\"$attr>$num</a>".
                "</sup>";
        }
        
        return "[^".$matches[1]."]";
    }
        
    
    ### Abbreviations ###
    
    protected function stripAbbreviations($text) {
    #
    # Strips abbreviations from text, stores titles in hash references.
    #
        $less_than_tab = $this->tab_width - 1;

        # Link defs are in the form: [id]*: url "optional title"
        $text = preg_replace_callback('{
            ^[ ]{0,'.$less_than_tab.'}\*\[(.+?)\][ ]?:  # abbr_id = $1
            (.*)                    # text = $2 (no blank lines allowed)    
            }xm',
            array($this, '_stripAbbreviations_callback'),
            $text);
        return $text;
    }
    protected function _stripAbbreviations_callback($matches) {
        $abbr_word = $matches[1];
        $abbr_desc = $matches[2];
        if ($this->abbr_word_re)
            $this->abbr_word_re .= '|';
        $this->abbr_word_re .= preg_quote($abbr_word);
        $this->abbr_desciptions[$abbr_word] = trim($abbr_desc);
        return ''; # String that will replace the block
    }
    
    
    protected function doAbbreviations($text) {
    #
    # Find defined abbreviations in text and wrap them in <abbr> elements.
    #
        if ($this->abbr_word_re) {
            // cannot use the /x modifier because abbr_word_re may 
            // contain significant spaces:
            $text = preg_replace_callback('{'.
                '(?<![\w\x1A])'.
                '(?:'.$this->abbr_word_re.')'.
                '(?![\w\x1A])'.
                '}', 
                array($this, '_doAbbreviations_callback'), $text);
        }
        return $text;
    }
    protected function _doAbbreviations_callback($matches) {
        $abbr = $matches[0];
        if (isset($this->abbr_desciptions[$abbr])) {
            $desc = $this->abbr_desciptions[$abbr];
            if (empty($desc)) {
                return $this->hashPart("<abbr>$abbr</abbr>");
            } else {
                $desc = $this->encodeAttribute($desc);
                return $this->hashPart("<abbr title=\"$desc\">$abbr</abbr>");
            }
        } else {
            return $matches[0];
        }
    }

}

// https://github.com/egil/php-markdown-extra-extended
class MarkdownExtraExtended extends MarkdownExtra {
    # Tags that are always treated as block tags:
    protected $block_tags_re = 'figure|figcaption|p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|form|fieldset|iframe|hr|legend';
        
    public function __construct() {
        /*
        $this->block_gamut += array(
            "doFencedFigures"   => 7
        );
        */

        $this->document_gamut += array(
            "doClearBreaks"     =>  100
        );
        
        parent::__construct();
    }

    public static function defaultTransform($text) {
        # try to take parser from the static parser list
        static $parser;

        # create the parser it not already set
        if (!$parser) {
            $parser = new MarkdownExtraExtended();
        }

        # Transform text using parser.
        return $parser->transform($text);
    }
    
    public function doHardBreaks($text) {
        # Do hard breaks:
        # EXTENDED: changed to allow breaks without two spaces and just one new line
        # original code /* return preg_replace_callback('/ {2,}\n/', */
        return preg_replace_callback('/ *\n/', 
            array($this, '_doHardBreaks_callback'), $text);
    }

    public function doClearBreaks($text) {
        return preg_replace("/\s*((?:<br \/>\n)+)\s*(<\/?(?:$this->block_tags_re|li|dd|dt)[^\d])/is",
            "\\2", $text);
    }


    public function doBlockQuotes($text) {
        $text = preg_replace_callback('/
            (?>^[ ]*>[ ]?
                (?:\((.+?)\))?
                [ ]*(.+\n(?:.+\n)*)
            )+  
            /xm',
            array($this, '_doBlockQuotes_callback'), $text);

        return $text;
    }
    
    public function _doBlockQuotes_callback($matches) {
        $cite = $matches[1];
        $bq = '> ' . $matches[2];
        # trim one level of quoting - trim whitespace-only lines
        $bq = preg_replace('/^[ ]*>[ ]?|^[ ]+$/m', '', $bq);
        $bq = $this->runBlockGamut($bq);        # recurse

        $bq = preg_replace('/^/m', "  ", $bq);
        # These leading spaces cause problem with <pre> content, 
        # so we need to fix that:
        $bq = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx', 
            array($this, '_doBlockQuotes_callback2'), $bq);
        
        $res = "<blockquote";
        $res .= empty($cite) ? ">" : " cite=\"$cite\">";
        $res .= "\n$bq\n</blockquote>";
        return "\n". $this->hashBlock($res)."\n\n";
    }

    public function doFencedCodeBlocks($text) {
        $less_than_tab = $this->tab_width;
        
        $text = preg_replace_callback('{
                (?:\n|\A)
                # 1: Opening marker
                (
                    ~{3,}|`{3,} # Marker: three tilde or more.
                )
                
                [ ]?(\w+)?(?:,[ ]?(\d+))?[ ]* \n # Whitespace and newline following marker.
                
                # 3: Content
                (
                    (?>
                        (?!\1 [ ]* \n)  # Not a closing marker.
                        .*\n+
                    )+
                )
                
                # Closing marker.
                \1 [ ]* \n
            }xm',
            array($this, '_doFencedCodeBlocks_callback'), $text);

        return $text;
    }
    
    public function _doFencedCodeBlocks_callback($matches) {
        $codeblock = $this->unhash($matches[4]);
        $codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);
        $codeblock = preg_replace_callback('/^\n+/',
            array($this, '_doFencedCodeBlocks_newlines'), $codeblock);
        //$codeblock = "<pre><code>$codeblock</code></pre>";
        //$cb = "<pre><code";
        $cb = empty($matches[3]) ? "<pre><code" : "<pre class=\"linenums:$matches[3]\"><code"; 
        $cb .= empty($matches[2]) ? ">" : " class=\"lang-$matches[2]\">";
        $cb .= "$codeblock</code></pre>";
        return "\n\n".$this->hashBlock($cb)."\n\n";
    }

    public function doFencedFigures($text){
        $text = preg_replace_callback('{
            (?:\n|\A)
            # 1: Opening marker
            (
                ={3,} # Marker: equal sign.
            )
            
            [ ]?(?:\[([^\]]+)\])?[ ]* \n # Whitespace and newline following marker.
            
            # 3: Content
            (
                (?>
                    (?!\1 [ ]?(?:\[([^\]]+)\])?[ ]* \n) # Not a closing marker.
                    .*\n+
                )+
            )
            
            # Closing marker.
            \1 [ ]?(?:\[([^\]]+)\])?[ ]* \n
        }xm', array($this, '_doFencedFigures_callback'), $text);        
        
        return $text;   
    }
    
    public function _doFencedFigures_callback($matches) {
        # get figcaption
        $topcaption = empty($matches[2]) ? null : $this->runBlockGamut($matches[2]);
        $bottomcaption = empty($matches[5]) ? null : $this->runBlockGamut($matches[5]);
        $figure = $matches[3];
        $figure = $this->runBlockGamut($figure); # recurse

        $figure = preg_replace('/^/m', "  ", $figure);
        # These leading spaces cause problem with <pre> content, 
        # so we need to fix that - reuse blockqoute code to handle this:
        $figure = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx', 
            array($this, '_doBlockQuotes_callback2'), $figure);
        
        $res = "<figure>";
        if(!empty($topcaption)){
            $res .= "\n<figcaption>$topcaption</figcaption>";
        }
        $res .= "\n$figure\n";
        if(!empty($bottomcaption) && empty($topcaption)){
            $res .= "<figcaption>$bottomcaption</figcaption>";
        }
        $res .= "</figure>";        
        return "\n". $this->hashBlock($res)."\n\n";
    }
}


